Dumbbell



FIG. 1 is a front, right and top perspective view of a dumbbell, showing my design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is another front, right and top perspective view thereof, in another state.

The broken lines depict portions of the dumbbell that form no part of the claimed design. 

CLAIM The ornamental design for a dumbbell, as shown and described. 